A massive multiple-input multiple-output (Massive MIMO) technology is a latest development MIMO technology. Massive MIMO technology can help reduce inter-cell interference and thermal noise, thereby improving spectral efficiency and expanding system capacity.
Currently, Massive MIMO technology mainly has two types of implementations. One is a channel reciprocity-based beamforming (BF) implementation. In the implementation, a base station uses a wide beam to receive pilot information sent by user equipment (UE), and performs precoding weighting on transmit data of different UEs based on channel responses of the UEs. However, this implementation requires that a physical beam corresponding to each channel be a wide beam. This implementation can be applied to a Time Division Duplex (TDD) system in which UE moves slowly.
The other implementation is a narrow beam-based BF technology. In this implementation, a physical beam corresponding to each channel is a narrow beam (that is, widths of physical beams in a horizontal direction and a vertical direction are only a few degrees), and each narrow beam corresponds to specific user equipment, and a BF weighted value of transmit data is obtained based on a predefined weighted value or a weighted value that changes slowly.
Unlike the channel reciprocity-based BF implementation, the narrow beam-based BF implementation can be applied to both the TDD system and a Frequency Division Duplex (FDD) system, and has a wide application range, and is a promising to Massive MIMO technology. Conventionally, the narrow beam-based BF implementation specifically uses a narrow beam traverse scanning method to determine a beam for data transmission, that is, the base station divides a spatial channel into K narrow beams, and successively transmits a scanning signal by using each narrow beam, and determines the beam for data transmission based on a scanning result fed back by UE. A quantity k of narrow beams is proportional to a quantity of antennas, and there is an extremely large quantity of antennas for the Massive MIMO technology. Consequently, the foregoing narrow beam traverse scanning method consumes extensive time, and results in large overhead.